My informant for this piece is an American of Scandinavian descent. He lived in Norway for a time during high school and learned the language while he was there. He also still keeps in contact with his host family from his time living there, and his son recently spent a year abroad there as well. His family participates in this tradition every year and has neighbors do it for them when they leave town for the holidays.
The legends and myths of trolls are very strong in Norway. They’re supposed to be tiny little tricksters, like gremlins. They live in barns–specifically red barns–so you’ll see a lot of red barns in Norway and Sweden because they bring good luck.
“On Christmas Eve you’re supposed to leave out what’s called ‘rømme grøt’ which is a porridge made with butter, cinnamon, and sometimes brown sugar. So on Christmas Eve the Fjøsnisse is supposed to come and eat it. If he eats it that means he’s happy with the rømme grøt you brought him, and he’ll bring you good luck–protect your livestock and barn for the year. But if he isn’t satisfied, he’ll cause mischief in your life for the whole next year!”
While this tradition is based around a belief in trolls, it also follows the principles of homeopathic magic. In leaving a bowl of porridge out for the Fjøsnisse, one is using the foods their farm produces in order to protect the sanctity of the farm itself. By using a part to protect the whole, believers in the Fjøsnisse practice homeopathic magic.